The present invention relates to the field of electronic equipment, and, more particularly, to an apparatus and method for protecting electronic equipment, such as from electrical surges.
Electrical power surges result in a substantial amount of damage to electronic equipment every year. Such surges may be the result of lightning or irregularities from a supply source, for example. Surges may enter the equipment through many external connections, such as power lines, coaxial cables, telephone lines, data lines, and low voltage control lines.
To protect against such surges, one traditional approach has been to attempt to dissipate surges using surge suppressor or arrestor devices, such as metal oxide varistors, Surgectors, carbon blocks, thyristors, and gas discharge tubes, for example. Unfortunately, such suppressor or arrestor devices may have a limited capacity to protect against large or repeated surges, and the equipment which remains externally connected may still be damaged.
Another more sophisticated and effective approach is to detect when a likelihood that a surge will occur, such as from an approaching lightning storm, for example. These detectors can disconnect the equipment from an external connection (a xe2x80x9cprotected statexe2x80x9d) while the threat of the surge (e.g., a lightning storm) remains present, and reconnect the equipment to the external connection when the threat has subsided. Examples of such more sophisticated protection systems may be found in U.S. Pat. Nos. 5,923,516 and 5,721,659, both entitled xe2x80x9cApparatus for Protecting Electronic Equipment and Associated Methodxe2x80x9dand assigned to the same assignee as the present invention, and both of which are hereby incorporated herein in their entirety by reference.
Widely used surge suppressors, and lightning rods (for facility protection) are typically completely ground dependent to perform their protection function. In other words, a low resistance electrical ground connection should be available and working at the time of the surge or lightning strike. In addition, a reliable low resistance ground connection is also important to reduce electrical noise in the protected equipment, and is also desirable for radio frequency transmitting and receiving equipment. Unfortunately, the resistance of the ground connection may become relatively high even if initially properly installed. If so, equipment connected to such a high resistance ground may then suffer damage in the event of an electrical surge and/or the equipment may experience increased noise, for example.
In view of the foregoing background, it is therefore an object of the invention to provide an apparatus and related method which can provide protection even where the resistivity of a ground connection varies and may become too high.
These and other objects, features, and advantages in accordance with the present invention are provided by an apparatus for protecting electronic equipment including an electrical ground connection in soil connected to the electronic equipment, a ground resistance sensor for sensing an electrical resistance of the electrical ground connection in the soil, and a dispenser for dispensing a resistance lowering material into the soil adjacent the electrical ground connection based upon the sensed electrical resistance being above a threshold. As a result, the electrical resistance of the ground connection is maintained at a sufficiently low level to allow power surges to dissipate through the ground connection and thereby avoid damage to the electronic equipment. Noise may also be reduced.
A protection device may further be included for selectively connecting and disconnecting the electronic equipment to and from an external connecting line, such as a power source, based upon the sensed electrical resistance. Hysteresis may be implemented to aid in this switching. In one embodiment, the dispenser may be set to dispense the resistance lowering material for a predetermined time, after which the protection device disconnects the electronic equipment from the power source if the sensed electrical resistance is higher than the threshold after the predetermined time. The resistance lowering material may be water, for example, and the threshold may be in a range of about 10 to 30 Ohms, for example.
Additionally, a power quality monitor may be connected to the protection device for disconnecting the electronic equipment from the power source responsive to surges in the power source. A lightning detector may similarly be connected to the protection device for disconnecting the electronic equipment from the power source responsive to lightning.
An alarm may additionally be included for providing an alert indication based upon the sensed electrical resistance being higher than the threshold. The alarm may be located at the electronic equipment or remote from the electronic equipment. The sensor may comprise one or more sensing electrodes positioned in the soil adjacent the electrical ground connection, in which case the sensor senses a resistance between the sensing electrodes or between a sensing electrode and the electrical ground connection. The dispenser may comprise at least one liquid delivery tube having an outlet adjacent the electrical ground connection.
A method for protecting electronic equipment according to the invention includes connecting the electronic equipment to an electrical ground connection in soil, sensing an electrical resistance of the electrical ground connection in the soil, and dispensing a resistance lowering material into the soil adjacent the electrical ground connection based upon the sensed electrical resistance being above a threshold.